Maintaining a proper pelvic posture and providing stability through the pelvis are critical to overall sitting posture. Freedom of movement can be enhanced by achieving a stable base of support. The optimum position for the pelvis is a slight anterior tilt. An effective pelvic support will prevent the pelvis from tilting posteriorly. A posterior pelvic tilt promotes rounding of the upper spine, which can lead to deformity. For a pelvis which posteriorly tilts, the top of the pelvis must be blocked from moving back and the bottom of the pelvis must be stabilized from moving forward. With adequate proximal support, less support is required distally. Therefore, with increased stability of the pelvis, the user is less dependent upon additional supports in order to maintain a functional, upright sitting posture. Individuals using wheelchairs need assistance to maintain pelvic stability.
The neutral posture of the pelvis is a dynamic state which should be allowed to move. Therefore, a rigidly stabilizing pelvic position is not desirable. Currently available pelvic supports either do not control undesired pelvic movement, or lock the pelvis in a static, non-functional position. Movements of the pelvis are critical to maintaining an active posture and should not be rigidly stabilized.
U.S. Pat. No. 6,213,558 (the “'558 patent”) discloses a pelvic stabilization device that attaches to a wheelchair and includes a pelvic support brace and an apparatus for attaching the pelvic support brace to the wheelchair. A pivot apparatus provides movement of the pelvic support brace with respect to the apparatus for attaching the pelvic support brace, the pelvic support brace being pivotable between a first, neutral position and a second, tilted position. A pivot return apparatus is attached to the pelvic support brace to return the pelvic support brace to the first, neutral position from the second, tilted position. A pivot limiting apparatus resists the amount of pivot of the pelvic support brace that is inducible by the pivot apparatus.
The pelvic stabilization device in the '558 patent includes a padded rear shell, two padded front shells, lateral hip pads, a pivot mechanism, a pivot limiter, a fore-aft lock, and attachment hardware. The rear shell supports the pelvis at the sacrum, the posterior superior iliac spines (PSIS's) and the sides of the pelvis. The width of the rear shell is adjustable to provide a custom fit for each user. The two front shells support the front of the pelvis at and around the anterior superior iliac spines (ASIS's). Lateral hip pads at the greater trochanter are designed to prevent the pelvis from sliding to the sides.
The pivot mechanism in the '558 patent allows anterior and posterior tilting of the pelvis. Adjustable centering springs help return the pelvis back to a neutral position and provide dynamic resistance to pelvic movement. The pivot limiter allows pivot movement of the pelvic stabilization device, and the user's pelvis, for only a predetermined range of motion. A separate adjustment for anterior and posterior tilt ranges allows adjustment of one independently of the other. The pivot limiter can be a mechanism separate from the pivot mechanism or, alternatively, the pivot limitation can be accomplished by the pivot mechanism. The pivot mechanism itself can limit pivot movement when, for example, the pivot mechanism is a spring, elastomeric or piston device. Pivot movement is then limited by the amount of force the user can provide against the pivot mechanism and still attain pivoting movement.